Pelletizing furnace



Dec. 22, 1959 P. L.. sTEFFENsEN PELLETIZING FURNACE 2 Sheets-Sheet 1Filed March 18, 1953 INVENTOR Perqy. Sie'enerz,

Dec. 22, 1959 P. STEFFENSEN PELLETIZING FURNACE 2 Shets-Sheet 2 FiledMarch 18, 1953 mw MT@ INVENTOR Per@ S'ff'rzla BY 20j@ ATTORNEY UnitedStates Patent O PELLETIZIN G FURNACE Percy Lea` Steffensen, Cornwall,Pa., assignor to Bethlehem Steel Company, a corporation of PennsylvaniaApplication March 18, 1953, Serial No. 343,138

1 Claim. (Cl. 263-29) My invention relates in general to a process andapparatusI for agglomerating line particles of iron oxide into pieces ofsufficient size for proper charging into a blast furnace or open hearthfurnace, and more particularly to a method, and furnace which havespecial advantages for performing the roasting operation of suchprocess.

The starting ore material which I prefer to use in the practice of myinvention is a moist tine concentrate of magnetite (Fe304), to which asmall amount of finely dividedfuel has been added; andthe desired endproduct consists of fairly large and uniform dry pellets of hematite(F8203)- Accordingly, there arewrequired two principal operations,namely, the formation of the ore balls in a balling drum or thelike,and'then the roasting of these balls at a temperature sufliciently` highto give the necessary strength and hardness to withstand subsequenthandling.

The operation of hardening these ore balls or pellets is.v preferablycarried out in a furnacel of the vertical shaft type wherein the` heatedore charge forms a continuous column of downwardly-moving material inthe stack.

Itis an object in this invention to provide means for maintaininguniform and continuous flow of the charge in such a furnace.

A further object is to provide agitator and Crusher means for assistingdischarge and preventing stoppages in the bottom discharge opening.

In the attached two (2) sheets of drawings:

Fig. 1 is a vertical section taken through one shaft of a furnace havingdual shafts and hoppers;

Fig. 2 is -a vertical section taken centrally through the lower portionsof the furnace shafts and the hoppers; and

Fig. 3 is a detail view, partly in section, of the air inlet and pelletagitating mechanism of the furnace.

Referring more particularly to the drawings inclusive, the furnace has arectangular outer shell 24 of steel plates, which shell is provided withconventional outer lstiffening members (not shown) and brick ties 25adapted for supporting the necessary thickness of insulating and hightemperature refractory brickwork 26. By means of a common dividing wall27 of refractory brick which extends vertically upward and terminates ina sloping peak 27 near the top of the furnace for the full length of thefurnace, said furnace is separated into twin shaft furnaces 28 and 29,which are operated and controlled practically as one.

Each of said shaft furnaces 28 and 29 is provided with combustionchambers 30 and 31 on opposite ends. Located centrally between thecombustion chambers in each shaft furnace and in spaced verticalalignment the end walls of each shaft define a top stack 32 having aslight upward taper, and below it an intermediate zone 33 and a lowerzone 34, terminating in a long steel hopper 35, all of which should berectangular in cross-section as shown in Fig. 1.

Each of said combustion chambers 30 and 31 is provided with a fuel oilburner 36, manholes 37, sight holes 38, an arched roof 39, and a bottomdust leg 40. Lower 2,918,267 Patented Dec. 22, 1959 and upper passages41 and 42 for admitting the air to be heated and for passing out theheated air connect each combustion chamber with the shaft below andabove the zone 33. The zones 33 and 34 have each essentially the shapeof an inverted truncated wedge with their respective side walls 43 and44 sloping at an angle preferably not exceeding about 20 from verticalto facilitate discharge. In dimensions, zone 33 will vary in width fromabout twice the bottom width of the stack 32 at the top of said zone tonot less than said bottom stack width at the bottom, and zone 34 may bemade somewhat wider. A short brickwork extension 45 carrying the bottomof said stack 32 slightly below the level of the roof 39 permits theproper travel of the hot gases and yet prevents the ore pellets fromentering the combustion chambers 30 and 31.

Air under pressure from a blower (not shown) is introduced centrallythrough horizontal lateral pipes 46 separated by partition plate 47 andthrough vertically arranged rows of louvres 48 on support members 49 atthe bottom of each shaft, and travels upward through the heated pelletsand lower passages 41 into the combustion chambers 30 and 31. Aninverted V-shaped cover 50- protects the above-described air inlet means46, 47 and 48 from the heavy downward pressure exerted by the descendingcharge and splits it centrally into two substantially equal parts.

Thermocouples 52 in passages 42 from the combustion chambers permitcontrol of air Volume and oil tlow to maintain a uniform heat line nearthe top of the charge and a constant combustion chamber temperature.

Referring to Fig. 3, agitator segments 53 having a plurality of breakerteeth 54 of Stellite or other hard alloy spaced at regular intervals ontheir upper faces are mounted at regularly spaced intervals on hollowair or water-cooled rocker shafts S5 extending horizontally intermediate between the cover 50 and bottom side walls 44 and parallelthereto. Said rocker shafts 55 are journaled through suitable air sealsin the side walls of the furnace as at 56 and adapted to be reciprocatedat intervals to break up any obstructing chunks of pellets by means ofthe arms 57 pivotally connected as at 58 to the connecting rod 59, whichin turn is pivotally connected by link 60 to crank 61 rotated by motor62.

The long steel hoppers 35 at the bottoms of the shaft furnaces have theform of inverted pyramids with substantially the same downward slope(about 20) as the lower side walls 44, and are provided near theirdischarge openings 63 with crusher discs 64 having evenly spacedhard-alloy teeth 65 entirely around their peripheries and withhard-alloy conical projections 66 on the side surfaces of the outerdiscs. Said discs are mounted for continuous rotation on a pair oftransverse shafts 67 which are joined by a coupling 68 and journaled inan air-tight manner in bearings 69 suspended by cross-beams '70 and 71and brackets 72. Gears 73 and 74 are driven by a gear reducer 75connected by a belt 76 or the like to a motor 77 mounted on l-beams 78.

It is preferable that the formation of large masses of` pellets beprevented, or that at least the size of any such masses be limited torelatively thin weak slabs which readily break apart as they move downthrough the: furnace, and are then easily broken down to individualpellets by agitator means 53 and 64.

I have found in practice that the formation of large; continuous massesor cakes of cohering pellets in the.- upper part of the charged materialin the furnace may be: quite effectively prevented by the exclusion offines from between the pellets in designated areas of the chargedmaterial. Suitable means for this purpose are the hori zontal angle bars174 shown in Fig. 1, disposed transversely across the furnace stack 32 aslight. distance above the top level of the charged pellets so as tointercept and direct the fall of the material being charged. The largeore pellets tend to roll before coming to rest, while the nes tend tocollect where they fall, so that in practice the desired distribution isobtained.

The operation of the furnace is continuous, the moist ore pellets beingcharged at the top of the shafts and moving slowly downward as the fusedand agglomerated product is discharged from the bottom hoppers. Theblowers (not shown) introduce through the pipes 46 the main volume ofair, which may be estimated approximately in the proportion of l2 cubicfeet of air to one pound of pellets, into the cooling zone 34 near thebottom. Here it meets the descending hot pellets and absorbs much oftheir heat. This ascending preheated air, at a temperature of about 1200F., divides when it reaches a point level with the bottom of thecombustion chambers 30 and 31,

part of it continuing on up through the shafts and part being divertedlaterally through the lower passages 41 and upward through saidcombustion chambers, wherein it is further heated to a temperature ofabout 1750 to 1850 F. The heated air then returns by means of the upperpassages 42 from the tops of the combustion chambers to the shafts,where it rejoins the air which has ascended through the shafts and heatsthe incoming pellets up to near the tops of the shafts. At the very topsof the shafts, much of the heat remaining in this ascendingv air isexpendedin removing moisture from the raw pellets introduced at the top,and air temperature drops to about 600 F.

The hard pellets at their discharge from the bottom of the furnace maybe regarded as cold for all practical purposes, since their temperatureswill not be much in excess of 150 F., constituting further proof of theeciency of the furnace as a heat interchanger between the hot pelletsand the incoming air.

If a furnace of rather limited capacity, say up to 275 tons per day, isdesired, a single stack and heating chamber p 4 tribution of the chargewill afford much better results than a single chamber of apparentlyequivalent capacity.

Although I have thus shown and described my invention hereinabove inconsiderable detail, I do not wish to be limited narrowly to the exactand specic details mentioned, but I may also use such substitutes,modifications or equivalents thereof as are embraced within the scopeand spirit of the invention and of the appended claim.

I claim:

An ore pellet roasting furnace comprising a substantially rectangularfurnace shaft having inwardly sloping opposite side walls, air inletmeans near the bottom of said furnace shaft intermediate the side walls,inverted V-shaped cover `means for protecting said air inlet means fromthe weight of the descending charge and dividing said charge intosubstantially equal parts, horizontally extending rocker shaftsintermediate said cover means and the side walls, a plurality of toothedsegments secured on said rocker shafts., and means for intermittentlyoscillating said rocker shafts with the segments thereon to break up thedescending charge.

References Cited in the le of this patent UNITED STATES PATENTS 182,419Cummings Sept. 19, 1876 742,037 Kearns Oct. 20, 1903 791,660 Walzel June6, 1905 865,658 Scott Sept. 10, 1907 1,164,761 Simmons Dec. 21, 19151,235,740 Terrace Aug. 7, 1917 2,280,571 Dionisotte Apr. 21, 19422,451,024 Ellerbeck Oct. 12, 1948 2,470,543 Azbe May 17, 1949 2,624,560Craig et al. Jan. 6, 1953 2,628,829 Ruiz Feb. 17, 1953 2,650,814 HowdenSept. 1, 1953 2,670,946 Royster Mar. 2,1954 2,676,095 DeVaney et al Apr.20, 1954 2,744,743 Beggs et al May 8, 1956 FOREIGN PATENTS 501,249 GreatBritain Feb. 23, 1939

